A comprehensive and straightforward methodology for optimal parameter design of Fractional Order control based Incremental Conductance (FOINC)-Maximum Power Point Tracking (MPPT) is developed in this paper. The main objective is to develop a more efficient, robust MPPT algorithm based on the integration between the fractional-order control and Incremental Conductance (INC) method. The integration between INC robustness and the accuracy of fractional-order can enhance the overall tracking performance in comparison to the conventional tracking techniques. Such integration ensures fast dynamics and high tracking accuracy for the Maximum Power Point (MPP) under tremendous climate variations. A small signal model for the whole system has been built to design the most appropriate order and gain of the fractional integrator for variable step size FOINC-MPPT. The ultimate gain (upper limit) of the controller has been specified properly via root locus plot before starting the optimization process to avoid falling in instability region. Radial Movement Optimization, as an optimization tool, is used for obtaining the optimal parameters of the fractional controller. The feasibility and effectiveness of the proposed FOINC-MPPT algorithm are validated under different climate conditions with slow and rapid changes in solar irradiance. Simulation results show that the proposed FOINC-MPPT algorithm is able to track the MPP accurately and rapidly in comparison with the conventional INC-based tracker.